Despite widespread agreement that high quality care can improve health and reduce costs for persons with diabetes mellitus, many persons with diabetes do not receive appropriate interventions to monitor their disease. One reason could be that many persons do not have continuity of care with a regular provider. The primary objective of this study is to examine whether high continuity of care has a positive impact on quality of care for persons with diabetes. The study has three specific aims: 1) to determine whether high continuity of care with an individual health care provider is associated with a higher likelihood of receiving appropriate interventions as recommended by the American Diabetes Association; 2) to determine if this association differs for persons with different health plan types or who see physicians of different specialties and 3) to determine if continuity with a provider group has a similar impact as continuity with an individual provider. Methods: Using a cross-sectional study design we will examine a 100 percent sample of administrative claims data for persons with diabetes in a large private health plan over a one-year period (7/95-6/96). We will select approximately 3000 persons ages 30-64 who are continuously insured in one of three health plan types (indemnity, preferred provider organization and point of service), have made at least three ambulatory visits and have at least two separate diagnoses of diabetes during the study year. We will measure continuity as the degree to which a person concentrates their care with an individual health care provider (for provider continuity) and with a provider group (for group continuity) during the study year, and will determine the specialty of the physician who provides the majority of ambulatory care during the same year (categorized as primary care, endocrinologist and other specialist). After controlling for demographics and case-mix, we will examine the impact of provider continuity and group continuity on the likelihood of receiving a glycosylated hemoglobin test, a cholesterol test, and an ophthalmoscopic exam during the study. We will also examine whether this impact differs across health plan types and physician specialties.